1. Field of the Invention
This invention relates to methods for concentrating surfactant solutions, particularly surfactant solutions comprising surfactant and water or brine. 2. Brief Description of the Prior Art
The oil industry has recognized for many years that the natural formation of an oil reservoir will produce only a portion of the crude oil originally in the reservoir. The oil industry has conducted extensive research on many different oil recovery methods in its efforts to economically recover more oil from petroleum reservoirs.
Surfactant flooding is one such method. Surfactant flooding involves injection of a solution containing surface-active agents or surfactants into the oil reservoir. The objective of surfactant flooding is to reduce the oil/water interfacial tension to an extremely low value, normally less than 1/10,000 of that present in a regular waterflood and thus greatly reduce the capillary forces which will otherwise trap oil. The use of the term "surfactant flooding" used herein shall be understood to include microemulsion flooding and other variations of waterflooding involving surfactant, including flooding where both surfactant and polymer are involved. For further discussion of surfactant flooding and microemulsion flooding, see C. C. Mattax, R. J. Blackwell, and J. F. Tomich, "Recent Advances in Surfactant Flooding," Proceedings of the Eleventh World Petroleum Congress 205-215 (1984).
Recent developments have led to increased confidence that surfactant flooding can recover significant amounts of incremental oil from a range of reservoirs with different rock and fluid properties. Such developments are discussed briefly in the above reference by C. C. Mattax, R. J. Blackwell and J. F. Tomich. However, surfactants are costly. The extent to which surfactant flooding can be applied economically has been uncertain.
Noting the need to minimize surfactant costs with surfactant flooding for enhanced oil recovery, J. B. Allison, et al. in U.S. Pat. No. 4,277,352, issued June 29, 1982, disclosed a method of reducing the expense related to the surfactant in such flooding. That patent explained that considerable quantities of surfactant injected into the reservoir as a recovery agent for enhanced oil recovery are produced with the crude oil in the form of an oil/water emulsion with the surfactant in the oil phase. The claimed method is one of treating the emulsion with a water soluble solubilizing agent, selected from a certain group of alcohols, or mercaptans, in an aqueous medium. The solubilizing agent extracts the surfactant from the emulsion, partitioning it into the aqueous medium. The patent further discloses recycling the recovered surfactant in the aqueous medium to the reservoir to continue the enhanced oil recovery process.
U.S. patent application Ser. No. 529,190 filed Sept. 6, 1983 by J. R. Bragg, et al discloses another method of breaking oil-water-(or brine)-surfactant emulsions produced from surfactant flooding. That method breaks the emulsion by controlling temperature and salinity within certain operable ranges. The emulsion is broken into an easily separable oil phase and a water phase with the surfactant in the brine or water phase. The brine phase, containing the surfactant, is then ready for use in additional oil recovery once separated from the oil phase by conventional means. The application notes, however, that there may be some desire to concentrate the surfactant for reservoir reinjection or for ease in transportation and handling.
The procedure for concentrating the surfactant in the brine disclosed in U.S. patent application Ser. No. 529,190 generally depends on the type of surfactant. Heating is disclosed for surfactants with an optimal salinity which decreases with increasing temperature. Cooling is disclosed for surfactants with an optimal salinity which increases with increasing temperature.